In many areas of medical treatment, it would be beneficial for a medical practitioner to be able to visualize a region for which treatment is contemplated and to accurately simulate the contemplated treatment. By visualizing the effect of the simulated treatment and altering the proposed treatment to optimize the results in a virtual setting, results can be improved and risks associated with the actual treatment can be reduced. This is particularly true in the case of invasive procedures such as surgery, biopsies and prosthesis implantation. The virtual setting would serve both as a tool for the guidance for actual treatment and as a “gold standard” for evaluation of the actual treatment and for follow-up management. Such a system can also provide an intuitive tool for medical training.
Preoperative imaging, such as by computerized tomography (CT), magnetic resonance imaging (MRI), ultrasound (US) and the like, is considered an important element in surgical planning. These conventional imaging technologies provide two dimensional (2D) image slices which illustrate key anatomic structures in a region of interest. However, the 2D slice images are limited in their ability to represent the spatial relationships between adjacent and interrelated structures. For example, a retro-displaced bifurcation point of carotid arteries might make stenosis analysis and plaque removal planning difficult. Three-dimensional (3D) information would be very helpful for planning surgical therapy.
Traditionally, spatial anatomical relationships could only be surmised by mentally integrating sequential 2D slice images. However, the advent of 3D computer graphical visualization techniques and high-resolution image scanning now allow 3D images (either surface-based or volume-based) to be constructed from sequential slice images and be displayed on a computer screen. Three-dimensional relationships between adjacent organs can be shown by interactively manipulating these virtual organs on the screen using a mouse or some other interactive devices. Over the past decade, many applications of such techniques in a number of areas of medicine, including otology, and neurology have been explored.
To achieve more accurate tissue classification and insight regarding tissue functionality, a series of single modality images and multi-modality images can be utilized. The single modality images can be of a common region acquired at different times or different orientations. In multi-modality images, the same region is imaged using two or more imaging technologies, such as CT, MRI and US in order to take advantage of the properties of each technology since a certain modality image may be sensitive to certain kind of tissues or their functions. By using single modality image series and multi-modality images, more information can be obtained, and limitations of certain modality can be mitigated.
The use of multiple image sets (including multi-modality images and or single modality image series) would be useful to perform virtual visualization and treatment planning for carotid artery stenosis and other conditions. Carotid artery stenosis is the most common cause of stroke, which is a major health care problem, that affects more than 700,000 Americans each year. In fact, this condition is the leading cause of disability and the third leading cause of deaths in the United States, after cardiovascular disease and cancer. Stenosis arises from the formation of plaque (consisting of calcification, cholesterol, and blood elements). The surgical procedure to remove plaque from a neck artery is called carotid endarterectomy. Prior to endarterectomy, the degree of stenosis needs to be measured and the position of the plaque must be localized. Currently available methods for evaluating carotid stenosis include, for example, carotid Doppler ultrasound and contrast angiography, which have been demonstrated for accurate determination of the degree of luminal stenosis. However, luminal narrowing is an indirect marker of plaque size and may underestimate the plaque burden as plaque may grow inside the vessel wall from the lumen towards the outer surrounding tissues. It is desirable that plaque size (both inwards and outwards boundary) and composition are accurately measured. These measures are of value since both plaque rupture and plaque removal carry risk. The measures relating to plaque composition and the likelihood of rupture can offer valuable risk assessment for the decision whether or not to proceed with a plaque removal operation.
Currently, MR data, CT data and US data each provide some insight into the structure, nature and position of stenosis within an artery. However, neither imaging technology alone is sufficient to provide a complete analysis of the size, composition and position of the plaque buildup. The benefits of these imaging technologies are largely complimentary and there would be a great benefit in having the ability to readily register images of a region using these complimentary technologies and to fuse the images into a single display. There is also a benefit in having the ability to register and fuse a series of single mode images to capture complimentary information contained therein.
In MR image data, the inter-slice and even intra slice image data often contains spatial inhomogeneity which adversely affects automated analysis of these images. Correction for spatial intensity inhomogeneities in inter- and intra-slices provides improved results in automated quantitative analysis of MR images. The inhomogeneities locally alter image intensity mean, median, and variance. It is known that they vary over time and with different acquisition parameters and subjects. For virtual treatment planning, a general purpose correction algorithm that can work for any scanning protocol and anatomy region is desirable. The concept of correcting image artifacts can be applied to the beam-hardening problem encountered in CT images as well as the attenuation distortion in US images.
Accordingly, there remains a need for improved medical treatment planning tools for optimizing the procedures and for evaluating the results.